The present exemplary embodiment relates to instruments or devices for collecting and sorting particles or samples, particularly from liquid or gaseous media. The exemplary embodiment finds particular application in conjunction with the separation and detection of biological agents, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Bio-agents dispersed either in aerosol form or in water are typically in such low concentrations that they are below the limit of detection (LOD) of even the most sensitive detection schemes. Yet, the ingestion of even a single bacterium may lead to fatal consequences. Accordingly, regardless of whether the sample is derived from aerosol or water collection, there exists a need to further concentrate the sample prior to detection.
Aerosol and hydrosol collection schemes typically sample large volumes of air at very high rates (150 kL/min and up), and use a cyclone-impactor design to collect particles having a size in the threat range and capture them in a wet sample of 5-10 mL volume. This supernatant is then used as the test sample for agent detection. In order to use currently available detection strategies, it would be desirable to further concentrate the hydrosol by another two orders of magnitude. For example, this could be achieved by collecting all the bio-particles in the sample volume within a smaller volume of 50-100 μL.
Contaminants in water are typically treated by several filtration steps to recover the sample for agent testing. After initial pre-filtration to remove larger vegetative matter, the sample is further concentrated by two to three orders of magnitude using ultra-filtration. This method of tangential flow filtration (TFF) is laborious as it may require multiple sequential steps of TFF; each step utilizing a filter of molecular weight (MW) cut-off that is 3-6× lower than the MW of the target molecules, and recycling of the retentate. The limiting factor for TFF is system loss, where there is a cut-off below which it may not provide any further improvement in concentration. The retentate at the end is approximately a 50 mL volume to be presented to the detector. It would be particularly desirable to further concentrate the retentate by up to another three orders of magnitude.
Field Flow Fractionation (FFF) is a technique that allows the separation of particles of different charge to size ratios (q/d) in a flow channel. This technique is useful in many fields ranging from printing to biomedical and biochemical applications. Separation is achieved because particles with different q/d ratios require different times to move across the flow channel, and therefore travel different distances along the flow channel before arriving at a collection wall. To obtain well-defined and separated bands of species with different q/d values, the particles are typically injected through a narrow inlet from the top of the channel. Total throughput depends on the inlet geometry and flow rate, which in turn affects the q/d resolution of the system.
FFF relies upon the presence of a field perpendicular to the direction of separation to control the migration of particles injected into a flow field. The separated components are eluted one at a time out of the system based on retention times, and are collected in a sequential manner. The separations are performed in a low viscosity liquid, typically an aqueous buffer solution, which is pumped through the separation channel and develops a parabolic velocity profile typical of Poissieulle flow. The process depends on controlling the relative velocity of injected particles by adjusting their spacing from the side walls. Particles with higher electrophoretic mobility or zeta potential will pack closer to the walls and therefore move slower than those that are nearer the center of the channel. In effect, particles move at different rates through the system based on zeta potential and size. Use of different separation mechanisms such as thermal, magnetic, dielectrophoretic, centrifugation, sedimentation, steric, and orthogonal flow has given rise to a family of FFF methods. Although satisfactory in many respects, there remains a need for an improved FFF separation technique.
The present exemplary embodiment contemplates a new and improved system, device, cells, and related methods which overcome the above-referenced problems and others.